As the circuits of a mobile phone are increasingly integrated, the thickness of a wiring substrate formed of layered dielectric plates becomes thinner. As a result, if a high frequency signal line is crossed with another signal line over a layer of the wiring substrate, both signal lines come close to each other at the cross point.
At the cross point where both signal lines come close to each other, a combined capacitance is formed by both wiring layers and an insulating material in between. Since the frequencies of the high frequency signals used for a mobile phone are in the GHz band, it is inevitable that the high frequency signals leak to other signal lines through this combined capacitance. The patent document 1 below discloses an example in which resistive elements are disposed immediately under and across the high frequency signal line so that other signal lines pass through the resistive elements, in order to reduce the leakage.
Patent document 1: JP-A No. 10-178305